The present invention relates to a display device which utilizes an emission of electrons into a vacuum space, which is defined between a face substrate and a back substrate; and, more particularly, the invention relates to a display device in which those are cathode lines having electron sources and control electrodes which control a quantity of electrons led out or emitted from the electron sources, and, at the same time, to a display device which exhibits stable display characteristics by maintaining a vacuum between the front substrate and the back substrate.
As a display device which exhibits high brightness and high definition, color cathode ray tubes have been popularly used conventionally. However, with the recent demand for the production of higher quality images in information processing equipment or television broadcasting, there has been an increasing demand for planar displays (panel displays) which are light in weight and require a small space, while exhibiting a high brightness and a high definition.
As typical examples, liquid crystal display devices, plasma display devices and the like have been put into practice. Further, more particularly, as display devices which can realize a higher brightness, it is expected that various kinds of panel-type display devices, including a display device which utilizes an emission of electrons from electron sources into a vacuum and is referred to as an electron emission type display device or a field emission type display device and an organic EL display, which is characterized by low power consumption, will be commercialized.
Among such panel type display devices, as an example of the above-mentioned field emission type display device, a display device having an electron emission structure, which was developed by C. A. Spindt et al, a display device having an electron emission structure of a metal-insulator-metal (MIM) type, a display device having an electron emission structure which utilizes an electron emission phenomenon based on a quantum theory tunneling effect (also referred to as “surface conduction type electron source,), and a display device which utilizes an electron emission phenomenon having a diamond film, a graphite film and carbon nanotubes and the like have been known.
Among these panel type display devices, the field emission type display device is formed by laminating a front panel, in which an anode electrode and a fluorescent material layer on an inner surface thereof, and a back panel, in which electron emission type cathodes and grid electrodes, which constitute a control electrode, are formed on an inner surface thereof with a distance of not less than 0.5 mm, for example, therebetween, wherein a sealed space is formed between both panels and the sealed space is evacuated to a pressure lower than an ambient atmospheric pressure or to a vacuum.
Recently, the use of carbon nanotubes (CNT) as a field emission electron source, which constitutes the cathodes of this type of planar display, has been studied. Carbon nanotubes are an extremely thin needle-like compound (more particularly, a so-called graphene sheet in which carbon atoms are coupled in a hexagonal shape is formed in a cylindrical shape). A carbon nanotube assembly which is formed by collecting a large number of carbon nanotubes is fixed to a cathode electrode. By applying an electric field to the cathode electrode formed of the carbon nanotubes, it is possible to emit electrons of high density from the carbon nanotubes at a high efficiency, whereby it is possible to constitute a flat panel display which is capable of displaying images of high brightness by exciting a phosphor with these electrons.
FIG. 13 is a schematic diagram illustrating the basic structure of a field emission type display device. CNT indicates the carbon nanotubes that are formed on a cathode (cathode electrode) K, A indicates an anode (anode electrode), and a phosphor PH is formed on an inner surface of the anode A. A grid electrode G, which controls the emission of electrons, is formed in the vicinity of the cathode K, and a voltage Vs is applied between the cathode K and the grid electrode G so as to emit electrons from the carbon nanotubes CNT. By applying a high voltage Eb between the cathode K and the anode A, the electrons e that are emitted from the carbon nanotubes CNT are accelerated, and the phosphor PH is excited, whereby a colored light L, which is dependent on the composition of the phosphor PH, is irradiated. Then, by controlling the quantity of electrons which are emitted based on the modulation voltage Vs applied to the grid electrode G disposed in the vicinity of the cathode K, for example, the brightness of the colored light L can be controlled.
FIG. 14 is a diagrammatic cross-sectional view illustrating an example of a field emission type display device. In this field emission type display (FED) device, a back substrate 1 which is formed of a glass plate, and a face substrate 2, which is also formed of a glass plate, are laminated to each other by way of a frame-like support body 3, which is interposed between both substrates. The support body 3 has a height of approximately 1 mm, for example, and it surrounds a display region so as to maintain a given distance between both substrates 1, 2. Further, the inside hermetic space is evacuated and sealed. Cathode lines 13, insulation layers 14 and grid electrodes 15 are formed on an inner surface of the back substrate 1, while anode electrodes 11 and phosphors 12 are formed on the face substrate 2. Carbon nanotubes of electron sources (not shown in the drawing) are provided on the cathode lines 13.
FIG. 15 is a diagrammatic plan view as seen from the back substrate 1 side of the field emission type display shown in FIG. 14. In the inside of the effective display region AR on the inner surface of the face substrate 2, phosphors R, G, B of three colors are arranged. In this example, respective pixels are defined by partitions 16. In a monochromic display, all phosphors are formed to have the same color.
With respect to a panel display which is constituted of two panels, as described above, a plasma display (PDP) or a panel display (MIM-FED) having a metal-insulator-metal field emission source has the same constitution. Although the explanation of the present invention will be directed hereinafter to a FED device as an example, the present invention is also applicable to a PDM device and a MIM-FED device. Further, the present invention is also applicable to a display device using surface conductive elements.
As an example of this type of panel display device, patent literature 1 (Unexamined Published Patent Japanese Application No. 2000-149788) discloses a device in which a getter housing chamber is separately provided to make up for a small evacuation conductance. Further, a technique which prevents the absorption of gas into the getter by introducing an inert gas into a high-temperature exhaust gas is disclosed in patent literature 2 (Unexamined Published Japanese Patent Application No. 2002-75202). Further, a proposal which carries out sealing and evacuation in a vacuum chamber is disclosed in patent literature 3 (Unexamined Published Japanese Patent Application No. 2002-56777). Further, a device which is further provided with getter support members, which control the scattering direction of the getter flash, is disclosed in the patent literature 4 (Unexamined Published Japanese Patent Application No. 2002-42638).